The long range goal of these studies is to understand how the organization and physical properties of the mammalian sperm plasma membrane change with maturation in the epididymis and capacitation in the female tract, and how these changes are related to physiological events which occur in the male and female tract. The sperm plasma membrane is extremely organized at two levels; (1) globally, in that membrane components are localized to specific regions of the sperm, and (2) molecularly as observed by ordered patterns of intramembranous particles. This order changes with maturation and capacitation. Thus an understanding of the processes of maturation and capacitation requires an understanding of how the sperm maintains and effects changes in this organization. To understand how the sperm effects and maintains this order; (1) we will use the technique of fluorescence photobleaching recovery (FPR) to determine if membrane "fluidity" of the plasma membrane is the same or different on different regions of the sperm, (2) we will also use photobleaching to determine if lipids of the various regions are free to diffuse and intermix, (3) we will use time lapse video intensified fluorescence microscopy to determine if egg and sperm lipids intermix at fertilization, (4) we will use FPR to study the restrictions to protein motion which lead to the localized destributions of membrane proteins, (5) we will consider the above issues (1), (2) and (4) as a function of maturation and capacitation, and (6) using time lapse video intensified fluorescence microscopy we will observe the processes which result in the redistribution of membrane components during maturation and capacitation.